CCNA: Cisco Certified Network Associate — Question 1093

When a switch receives a frame from an unknown source MAC address, which action does the switch take with the frame?

Answer options

• A. It sends the frame to ports within the CAM table identified with an unknown source MAC address.
• B. It floods the frame out all interfaces, including the interface it was received on.
• C. It associates the source MAC address with the LAN port on which it was received and saves it to the MAC address table.
• D. It attempts to send the frame back to the source to ensure that the source MAC address is still available for transmissions.

Correct answer: C

Explanation

The correct answer is C because when a switch encounters a frame with an unknown source MAC address, it learns the address and associates it with the port it was received on, adding it to the MAC address table for future reference. Option A is incorrect because the switch does not send the frame to the CAM table; it learns from it. Option B is wrong as flooding is used for unknown destination MAC addresses, not source addresses. Option D is not a standard behavior for switches; they do not send frames back to confirm MAC addresses.